Production of neutral Higgs bosons associated with Z-boson and photon in 2HDM at future lepton colliders

Abstract

Inspired by precision tests of the Standard Model in future lepton colliders, the numerical analysis of the following scattering processes, $e^+e^- \rightarrow Z h^0\gamma$ and $e^+e^- \rightarrow Z H^0 \gamma$, are carried at the tree level including all possible diagrams in the two-Higgs-doublet model (2HDM). This model has many free parameters, but the parameters which take part in the scattering amplitudes of these two processes are primarily the mixing angle parameter, $s_{\beta-\alpha}$, and the masses of the neutral Higgs bosons, ($h^0, H^0$). Therefore, measuring the production rates of $Z h^0\gamma$ and $Z H^0 \gamma$ final states open another test for the scalar sectors of the 2HDM. The numerical analysis is performed under the current experimental constraints. The production rates and the asymmetry in the forward-backward direction are presented as a function of the center-of-mass energy covering the future lepton colliders. The unpolarized cross-section gets up to 6.19 (4.86) fb at $\sqrt{s} = 350$ (500) GeV and 0.164 (0.157) fb at $\sqrt{s} = 350$ (500) GeV for $e^+e^- \rightarrow Z h^0\gamma$ and $e^+e^- \rightarrow Z H^0 \gamma$, respectively. The polarization of the incoming $e^+e^-$ beams are studied for various configurations, and it enhances the cross-section by a factor of 1.78 in both processes for $P_{e^+,e^-}=(+0.6,-0.8)$.